The present invention relates in general to wireless telecommunications, and more particularly to the utilization of standard home/office telephone sets in conjunction with cellular transmission technology.
The vast number of residential telephone sets require the use of a twisted pair metallic telephone line that extends between the telephone set and a remote central office switching system. For convenience and purposes of future expansion, two such pairs of subscriber lines are installed and connected to a subscriber""s residence, even if only a single telephone set is employed. While the infrastructure of such type of communication medium is well established, there are numerous shortcomings. For example, the installation of the twisted pair lines is costly, time consuming and susceptible to periodic maintenance. Moreover, the twisted pair lines were designed for voice-grade telecommunications and not for high speed data transmissions. In some instances, the bandwidth of the twisted pair line is limited by filters and other circuits connected to the line at the central office. The standard telecommunication services provided by way of such type of public switched telephone network is commonly known as xe2x80x9cplain old telephone servicexe2x80x9d (POTS). According to the routine POTS service, people have become accustomed to the procedures of making telephone calls using the customary call progress signals which include dial tone before entering digits, busy tone to indicate a busy called party, fast busy for a busy trunk line, etc.
More recently, the wireless telecommunication technology has been implemented to facilitate mobility of the subscribers while utilizing the same and additional telecommunication features. Mobile radios are one example, and the cellular telephone technology is another example of the wireless telecommunication technology. This type of technology does not require the installation of copper wires for carrying voice and data information. However, the wireless telephones themselves are more costly than the standard POTS telephone handsets, even the cordless telephone sets commonly available today. There exists many different types of wireless protocols for transmitting voice and data between the cellular telephones and remote base stations.
One popular wireless protocol is the code division multiple access (CDMA), more specifically described in the specification IS-95, promulgated by the Telecommunication Industry Association. In this type of spread spectrum cellular transmission, there are many frequency channels, and multiple users can simultaneously utilize the same frequency channel. Moreover, each of the multiple users of a particular frequency channel transmits at a different power level. If the proper power transmission levels are maintained, each user allocated to a frequency channel can obtain access to the channel. However, in the event one or more of the cellular transceivers transmits at a power level greater than that initially allocated, other users of the frequency channel are denied use thereof. The capacity of the cellular system is thereby compromised.
Remote cellular base stations defining the various geographical cells monitor signal level transmissions from each cellular transceiver in the operating vicinity, and adjust the power level thereof to achieve a predefined level. The signal levels of the wireless transmissions received by a remote cellular base station can vary due to the user moving closer or further away from the base station, due to obstacles, multi-path reflections of the signal, etc. Because the power adjustments made by the base station on the cellular transceivers power levels are only periodically adjusted, there are times when the transmitted power of a user is in excess of what it should be. For example, if obstacles between the transceiver and the cellular base station cause the signal level of the transmission to be reduced when received by the base station, the base station will transmit coded information to the transceiver of a user to increase its power level. However, if the transceiver thereafter moves so that the obstacle is no longer between the transceiver and the base station, the signal level will be much greater than what it should be. During this time period, one or more other subscribers cannot be assigned to this frequency channel. Cellular system capacity is thus compromised.
Attempts have been made to integrate the cellular technology with home telephone use. This technology is termed xe2x80x9cWireless Local Loopxe2x80x9d, and is set forth in U.S. Pat. No. 5,799,254 issued to Karmi et al; U.S. Pat. No. 5,790,631 issued to Minarczik et al; U.S. Pat. No. 4,658,096 issued to West, Jr., et al. The temporary installation of a wireless local loop communication system can provide expedited service in disaster areas, or other areas where the POTS system has been damaged. Various features of the wireless local loop system allow the user to utilize standard POTS equipment and techniques without having to learn the more complicated procedures necessary for cellular telephone use.
From the foregoing, it can be seen that a need exists for a method and apparatus for allowing a home or office occupant to be able to utilize a movable or mobile telephone set with the cellular technology, and not adversely affect the user capacity of the wireless cellular system. Another need exists for interfacing standard cordless telephone equipment with cellular transceiver equipment.
The embodiments of the invention disclosed herein overcome the disadvantages of the corresponding prior art techniques, devices and systems. In one embodiment of the invention, there is disclosed a communication system in which a cellular transceiver is integrated with a cordless telephone. Preferably, the communication system is housed in a single module having a fixed transceiver and cordless telephone antenna. In this arrangement, the transmission power level utilized between the cellular transceiver and a remote cellular base station is maintained at a constant level, irrespective of the movement by the user of the cordless telephone handset.
A subscriber line interface circuit (SLIC) is employed to provide telephone service to other telephone sets connected to the communication system by telephone lines and RJ-11 jacks. The microprocessor in the cellular transceiver controls the SLIC module to provide POTS-type service to the telephone sets. In addition, the microprocessor controls monitor circuits that monitor the telephone line and RJ-11 jack for foreign voltages, and on finding the same, the SLIC module is prevented from providing service to the telephone sets connected thereto.
In accordance with another feature of the invention, the user of the cordless telephone need only communicate utilizing the standard POTS-type of procedures, while yet being allowed the capability of cellular system service. Metallic twisted pair subscriber lines and the corresponding installation and service thereof is not required.
The cellular transceiver is interfaced with the cordless telephone base unit by way of hardware and software interfaces. A processor in the cellular transceiver and a processor in the cordless telephone base unit communicate by way of a bidirectional data bus. A protocol of primitives are passed between the microprocessors to carry out bidirectional communications between the cordless telephone handset and the cellular transceiver. A layered software structure in the microprocessors of the cellular transceiver and the cordless telephone base unit controls the operation of the devices to thereby enable communications and corresponding signals to be passed between the different types of communication equipment.
A subscriber line interface circuit (SLIC) is employed to provide telephone service to other telephones connected to the communication system by telephone lines and RJ-11 jacks. The microprocessor in the cellular transceiver controls the SLIC module to provide POTS-type service to the telephone sets. In addition, the microprocessor controls monitor circuits that monitor the telephone line and RJ-11 jack for foreign voltages, and on finding the same, the SLIC module is prevented from providing service to the telephone sets connected thereto.